Hyperlipidemia is thought to be one of the causes for diseases such as hypertension, arteriosclerosis, and myocardial infarction. Certain azulene derivatives capable of being used as a hypolipidemic agent are already known, for example, 1-methoxycarbonyl-3-ethyl-7-isopropylazulene (JP-A-156611/1985) and certain formyl-substituted azulenes (EP 182491). Also, 6-isopropyl azulene 1-carboxylic acid methyl esters are known as intermediates in preparing 1,4-dimethyl-6-isopropyl azulene (Miyoshi et al, 43rd Ann. Meeting, Chem. Soc. of Japan, 1981, Abstract II p. 889), but not for any pharmaceutical use.